For a number of years, it has been known that various microorganisms exhibit biological activity useful in controlling plant diseases. Although progress has been made in the field of identifying and developing biological pesticides for controlling various plant diseases of agronomic and horticultural importance, most of the pesticides in use are still synthetic compounds. Many of these chemical fungicides are classified as carcinogens by the EPA and are toxic to wildlife and other non-target species. In addition, pathogens may develop resistance to chemical pesticides (see, e.g., Schwinn et al., p. 244, ADVANCES IN PLANT PATHOLOGY: PHYTOPHTHORA INFESTANS, THE CAUSE OF LATE BLIGHT OF POTATO (Academic Press, San Diego 1991)).
Biological control offers an attractive alternative to synthetic chemical fungicides. Biopesticides (living organisms and the naturally produced compounds produced by these organisms) can be safer, more biodegradable, and less expensive to develop.
Screening programs have identified certain Bacillus sp. (B. sp. includes B. subtilis, B. cereus, B. mycoides, B. anthracis and B. thuringiensis) strains which exhibit antifungal activity. (See, e.g., Stabb et al. (1994) Applied Environ. Microbiol. 60(12):4404-4412). These strains have been shown to produce zwittermicin-A and/or antibiotic B (now known as kanosamine (Milner et al. (1996) Appl. Environ. Microb. 62:3061-3056)), two antibiotic agents which are effective against the soil borne disease "damping-off" caused by Phytophthora medicaginis, Phytophthora nicotianae, Phytophthora aphanidermatum or Sclerotinia minior. (See, Stabb et al., supra). Zwittermicin-A is a water-soluble, acid-stable linear aminopolyol molecule. (see, He et al. (1994) Tetra. Lett. 35(16):2499-2502).
U.S. Pat. No. 5,049,379 to Handelsman et al. describes how zwittermicin A-producing B. cereus can be used to control the below-ground seedling diseases "root rot" and "damping off" in alfalfa and soybean. When the seed is coated with zwittermicin-A produced by B. cereus ATCC 53522, the pathogenic activity of the root rot fungus is inhibited. Similarly, application of spore-based formulations of certain B. cereus strains to soybean seeds or the soil surrounding the seeds has been shown to improve soybean yield at field sites. (See, Osburn et al. (1995) Am. Phytophathol. Soc. 79(6): 551-556). Methods of applying biopesticides are well known in the art and include, for example, wettable powders, dry flowables, microencapsulation of effective agents, liquid or solid formulations and antibiotic fractions obtained from suitable cultures. (See, e.g., U.S. Pat. No. 5,061,495 to Rossall or U.S. Pat. No. 5,049,379 to Handlesman).
Smith et al. (1993) Plant Disease 77(2):139-142 report that the activity of the soil-borne fungus, Pythium aphanidermatum, that causes cottony cucumber leak can be suppressed using zwittermicin-producing B. cereus strain UW85. Leifert et al. (1995) J. Appl. Bacteriol. 78:97-108 report the production of anti-Botrytis and anti-Alternaria brassicicola antibiotics by two Bacillus strains, B. subtilis CL27 and B. pumilis CL45. The whole broth and cell-free filtrates were active against Botrytis and Alternaria in vitro tests and were active against Botrytis in in vivo small plants tests on Astilbe.
Sholberg et al. (1995) Can. J. Microbiol. 41:247-252, Swinbume et al. (1975) Trans. Brit. Mycol Soc. 65:211-217, Singh and Deferral (1984) Trns. Br. Mycol Soc. 83:487-490, and Ferreira, et al. (1991) Phytopathology 81:283-287 disclose the use of Bacillus sp. and Bacillus subtilis as biocontrol agents of fungal plant pathogens. Baker et al. (1983) Phytopathology 73:1148-1152 also report on an antifungal Bacillus subtilis for use on plant pathogens. Pusey et al. (1988) Plant Dis. 72:622-626, Pusey and Robins (U.S. Pat. No. 5,047,239) and McKeen et al. (1986) Phytopathol. 76:136-139 disclose control of post harvest fruit rot using B. subtilis. McKeen et al., supra, have shown that antibiotics similar to the low molecular weight iturin cyclic polypeptides contribute to this fungicidal activity of B. subtilis.
Stabb et al. (1990) tested 11 Bacillus thuringiensis strains for zwittermicin production. Only one strain (BGSC4F1) tested positive for zwittermicin. This strain was weakly active against alfalfa damping off. There are no reports, however, of strains of Bacillus thuringiensis with broad fungicidal and bactericidal activity.